The present invention relates to a stereo loudspeaker system comprising a unitary enclosure having a rear wall intended to be oriented towards a reflecting wall, a front wall positioned opposite thereof, side walls, a top wall and a bottom wall, said stereo loudspeaker system including an even number of low-frequency loudspeakers (woofers) which are disposed symmetrically in the rear wall at an angle to each other.
The combination of an enclosure with a number of loudspeakers and possibly some electronic components such as a separating filter present in that enclosure, is in general referred to as a speaker box. This expression or the expression xe2x80x9cboxxe2x80x9d, in the above meaning, will also be used in the remainder of this description. Known stereo loudspeaker systems in general comprise at least two speaker boxes which are spaced from each other, and which, each include, in many cases, several loudspeakers, each of which operates over a part of the acoustic frequency spectrum between approximately 10 Hz. and 20,000 Hz. Many loudspeaker systems even comprise pure than two speaker boxes is order to make the stereo impression as perfect as possible. The function of speaker boxes is to produce sound, which implies that in fact the speaker box preferably should not take up any space at all. In practice, speaker boxes of course always have a certain volume, and in fact, a relatively large volume is more advantageous than a relatively small volume for a good sound reproduction and a good stereo impression.
A particularity of the perception of the stereo impression of a sound installation, is that the human ear is relatively insensistive to the precise location of the low-frequency loudspeakers or woofers. This offers the possibility to position one or more woofers in a central speaker box, so that the loudspeakers reproducing the midrange sounds (squawkers) and those reproducing the high-frequency sounds (tweeters) can be positioned, together or separately, in separate speaker boxes for the left and right stereo channel, each of which requires a much smaller volume than when these would include a woofer as well. Accordingly, stereo installations are known comprising a unitary enclosure, the rear wall of which incorporates two woofers which are oriented towards the wall of a listening room. Hence, this type of stereo loudspeaker systems thus requires at least three speaker boxes: a central speaker box including woofers and at least two other speaker boxes for the left and the right stereo channel, respectively.
The invention aims to provide a stereo installation system of the type mentioned is the preamble, which takes up less space than comparable known stereo installations and which allows more freedom with respect to the positioning of the stereo loudspeaker system. To this end, the invention is characterized in that, in addition to the even number of symmetrically arranged woofers, the system includes an even number of other loudspeakers which are all located in said unitary enclosure, and in that the loudspeakers are arranged approximately next to each other in a single loudspeaker plane or, at least some of them, in pairs at equal distances from said loudspeaker plane.
The stereo loudspeaker system according to the invention thus merely comprises a single, unitary enclosure which includes all the necessary loudspeakers in the above mentioned arrangement. It has been found that in this way an excellent stereo impression can be obtained by means of only one speaker box.
It is known to use stereo speaker boxes comprising so-called bass reflex pipes in order to improve the reproduction of low-frequency sounds. An embodiment of the invention comprising bass reflex pipes is characterized in that an even number of symmetrically arranged bass reflex pipes arc disposed in the rear wall between the woofers, and in that the bass reflex pipes are located in said loudspeaker plane, or at least some of them in paris at equal distances from said loudspeaker plane.
In practice, this arrangement has been found to be important for achieving a good low-frequency sound reproduction in the stereo loudspeaker system according to the invention, which can moreover be further improved in this respect using the following embodiment, which is characterized in that the angle between the woofers is within the range of 55 to 70 degrees, and is preferably about 62 degrees. It has been found that, as a result of the inclined disposition of the woofers at the above-mentioned angle, an optimum distribution of low-frequency sound reproduction is obtained.
For the reproduction of the part of the acoustic frequency spectrum above the low-frequency range, a further embodiment of the invention is important in which suitable frequency filters may be used and which is characterized in that one half of the loudspeakers present can be connected to the left stereo channel aid the other half can be connected to the right stereo channel of a stereo amplifier. in that a midranqe loudspeaker (squawker) that can be connected to the left stereo channel, and a high-frequency loudspeaker (tweeter) that can be connected to the left stereo channel, as well as a squawker that can be connected to the right stereo channel, and a tweeter that can be connected to the right stereo channel, are disposed in the front wall of the enclosure, in that the two tweeters are disposed between the two squawkers, in that the tweeter for the right stereo channel is disposed between the squawker for the left stereo channel and the tweeter for the left stereo channel, and in that the tweeter for the left stereo channel is disposed between the squawker for the right stereo channel and the tweeter for the right stereo channel.
This special arrangement of squawkers and tweeters has been found important for obtaining a good and satisfying stereo impression. Moreover, it had been found that the positioning of the loudspeaker system and the position of the listener in a listening room with respect to the loudspeaker system are less critical with this arrangement.
A further improvement of the above embodiment can be obtained by means of yet another embodiment, which is characterized in that the squawkers are disposed in front wall panels which are oriented at an angle to each other, and in that each of the tweeters is disposed in a front wall panel which is, at least approximately, parallel to the front wall panel in which the squawker of the corresponding stereo channel is disposed.
In order to use the volume in the unitary enclosure as well as possible, another embodiment of the invention is important, which is characterized in that the acoustic space enclosed in the enclosure is at least shared by the woofers, and in that one or more conductors made of a rigid material are located within the acoustic space for the purpose of bass reflection.
The squawkers and tweeters are usually provided with airtight envelopes at the rear side thereof so that, in acoustic respect, they are not located within the same space as the woofers. As the airtight envelopes are relatively thin, the greater part of the volume enclosed in the enclosure is available as acoustic space to the woofers and any bass reflex pipes present. By a correct positioning of one or more conductors, the volume present can be used optimally so as to achieve the best possible reproduction by the woofers themselves and by the bass reflex pipes.
In many cases, the reflecting walls behind the box consist of suitable rigid or at least advantageously reflecting walls of a listening room, such as a living room or the like. It is also possible to use an embodiment of the invention which is characterized in that the reflecting wall consists of a reflector which is connected to the enclosure. Consequently, the box is not dependent on the reflecting properties of the wall of a listening room.
It has been found in practice that the positioning of the box relative to the wall is quite critical for obtaining a good sound quality. An embodiment of a box having a rear wall in the form of a reflector has some advantages in this respect and is characterized in that the reflector is mounted at a predetermined optimum distance from the enclosure which is determined on the basis of sound quality criteria. Preferably, yet another embodiment is used, which is characterized in that the reflector is connected to the enclosure in an inseparable fashion. As a result, the optimum positioning of the reflector relative to the rear wall of the box is continuously assured.